Photoreactions refer to chemical reactions induced by light. One type of photoreaction is photocatalysis. In a typical photocatalytic process, light is absorbed by an adsorbed substrate to create electron-hole pairs, which generate free radicals (e.g. hydroxyl radicals: *OH) along with oxygen. These free radicals are able to undergo very useful secondary reactions. For example, the free radicals are able to react with organic contaminants to decompose them. Therefore, such a reaction has an ability to clean air, wherein offensive, odourus, harmful gases, or the like, are decomposed to harmless forms leading to a reduction in the quantity of these unwanted elements in the surroundings.
Various materials have been used for photocatalytic process. One such material is titanium dioxide (TiO2). Usually, TiO2 absorbs Ultraviolet (UV)* radiation from sunlight or illuminated light source (fluorescent lamps), thereby producing electrons and holes. The electron of the valence band of titanium dioxide becomes excited when illuminated by light.
The excess energy of this excited electron promotes the electron to the conduction band of titanium dioxide therefore creating the negative-electron (e−) and positive-hole (h+) pair. The photocatalytic oxidation of an organic species often proceeds via adsorption of the pollutant on the surface of the catalyst, followed by direct subtraction of the pollutant's electrons by positively charged holes. Another possible way is oxidation with OH radicals, generated from water of the aqueous environment, which takes place at the catalyst surface or in its vicinity. Both reactions may proceed simultaneously and which mechanism dominates depends on the chemical and adsorption properties of the pollutant. Therefore, it will be appreciated that there is a reasonable need to improve the photocatalysis process so as to provide means to clean pollutants from ambient air.
Various ways are known for improving the utility of the photocatalysis process. For example, the utility of the process could be increased by developing new and better photocatalytic materials, which have better rates of cleaning the pollutants. Another way of improving the utility of the process is by developing new techniques by which better quality photocatalytic materials can be derived at a cheaper rate. Yet another way includes finding out efficient ways of increasing the practicability of such a process so as to make it easily available commercially.
Therefore, there is a continuous need for improving the photocatalysis process for variety of applications. More particularly, there is a need of water soluble photocatalytic materials, making them easily applicable on various articles by conventional process. Further, there is a need of having photocatalytic materials that have high rate of de-odourizing and purifying its surroundings.
Furthermore, there is a need of having photocatalytic materials capable of absorbing the ultra violet light from the visible light spectrum, thereby neutralizing the bad effects of ultra violet light. Additionally, there is a need of having photocatalytic materials which are easy to obtain, durable and inexpensive to manufacture.
Moreover, there is a need for manufacturing articles by applying photocatalytic materials which can be easily used by mankind and such articles with photocatalytic materials coated on them may act as a good absorbent of ultra violet light from the visible light spectrum, cleaning ambient air without degrading the luminance of light.
More specifically, there is a need for manufacturing portable articles which have photocatalytic activity, and can be easily placed at corners of various enclosed places, such as rooms, cars, and the like, for purifying the ambient air in these enclosed spaces. Such effect is supposed to bring significant advantages to the health of humans and other mammals breathing in these enclosed spaces.